In a conventional semiconductor manufacturing process, a plasma processing apparatus using a high frequency glow discharge of a reaction gas (a processing gas) introduced into a processing chamber has been widely used in order to perform microprocessing on a surface of an object to be processed, e.g., a semiconductor wafer (hereinafter, referred to as a “wafer”). Among those plasma processing apparatuses, the so-called parallel plate plasma processing apparatus in which electrodes are opposedly arranged to face each other at an upper and a lower portions of the processing chamber is appropriate for processing of a large diameter wafer.
The parallel plate plasma etching processing apparatus 25 has elevatable upper and lower electrodes arranged parallel to each other in a processing chamber. The lower electrode also serves as a mounting table of a wafer. When high frequency powers having different frequencies are respectively applied to the upper electrode and the lower electrode, a glow discharge is generated between the lower electrode on which the wafer is loaded and the upper electrode, so that the reaction gas introduced into the processing chamber becomes plasma. Ions of the plasma collide against a surface of the wafer due to an electric potential difference generated between the electrodes, thereby etching a film, e.g., an insulating film, formed on the wafer surface.
Around the peripheral portions of the lower electrode and the upper electrode, a focus ring surrounding the wafer loaded on top of the lower electrode and a shield ring are arranged, respectively. By using the two rings, the plasma generated between the upper and the lower electrodes is converged on the wafer, and, accordingly, the plasma density above the wafer surface becomes uniform.
During the manufacturing process of a semiconductor, various reaction gases for forming or removing films are introduced into the processing chamber of the plasma processing apparatus. Although it is desirable that the reaction gases react completely as intended, parts of the reaction gases are discharged out of the processing chamber without having any reaction and parts of the reaction gases generate undesirable reaction by-products. Further, such reaction by-products adhere to various portions of the processing chamber. Hereinafter, the undesirable reaction by-products adhered to the processing chamber are referred to as “deposits”.
The deposits can be removed by cleaning the processing chamber of the plasma processing apparatus. However, once the plasma processing apparatus starts operation and repeats plasma processing on wafers, new deposits are generated and gradually accumulated in the processing chamber.
Especially, in case the deposits are adhered around the peripheral portions of the upper and the lower electrodes, e.g., on the focus ring and the like, the deposits may cause an abnormal discharge soon after a plasma ignition. Consequently, subsequent film deposition or film removing process may not be appropriately carried out. Further, an emergency stop of the plasma processing apparatus may be required to clean the processing chamber.
As a solution to such problem due to deposits, Japanese Patent Laid-open Publication No. 1995-58028 discloses a substrate mounting table of an ECR-CVD apparatus in which an electrode and its surrounding region are fixed on a base plate.
In the invention disclosed in the Japanese Publication supra, the surrounding region of the electrode is made of aluminum oxide and the like and, further, fixed on the base plate, so that it acquires rigidity, acid resistance and insulating property. Therefore, by repeatedly cleaning the surrounding region of the electrode, it is possible to maintain same in a clean state free of the deposits. Further, a time required to clean the surrounding region of the electrode can be shortened.
However, in the above prior art, even though the cleaning process for removing deposits from the surrounding region of the electrode can be facilitated, the plasma processing apparatus is still required to be stopped for the removal of the deposits. In an up-to-date semiconductor manufacturing process for forming a multilayer structure on a large diameter wafer, deposits tend to grow faster than before. Therefore, if the plasma processing apparatus is stopped frequently to remove the deposits, the throughput thereof can be substantially deteriorated.